Time delay relay device



April 18, 1961 w. F. HORTON 2,980,826

TIME DELAY RELAY DEVICE Filed May 1, 1957 States P nt TIME DELAY RELAY DEVICE WilliamF. Horton, Pacific Palisades, Califi, assignor to Lear, Incorporated Filed May 1, 1957, Ser. No. 656,386

' 3 Claims. (31. 317-1485) In time delay relays of the type heretofore known, the

means, for controllably delaying the application of power from a source to the relay control coil is undesirably dependent upon ambient temperature, as in the eddy current type time delay relay, or upon voltage, as in the thermal type time delay relay. Difficulty is also experienced ininstantaneously resetting the delay means, independent of delay time, so as to permit an operator to de-energize the relay and instantaneously re-initiate the delay time. Furthermore, the time delay relays of the prior art are characterized by undue complexity, size and weight, all of which contribute materially to the cost of such a device.

It is an object of this invention to provide an improved time delay relay, in which dependency on ambient temperature and voltage is minimized, and in which the delay time can instantaneously be re-initiated upon de-energization of the relay.

A further object of this invention is to provide an improved time delay relay utilizing a semiconductor to establish the delay period, which is characterized by extremely simple desi of a minimum number of component parts, and which is much smaller, lighter in weight and less expensive than time delay relays of the prior art.

The above and other objects and advantages of this invention will become apparent from the following description, taken in conjunction with the accompanying drawing, in which a preferred embodiment is illustrated by Way of example. The scope of the invention is pointed out in the appended claims. In the drawing,

The sole figure is a schematic diagram of a time delay relay employing a semiconductor, in accordance with this invention.

Briefly, this invention includes a transistor having its emiter-collector path connected in series with a switch between a D.-C. source and the relay coil, and an RC (resistor-capacitor) network in circuit with the emitter and base electrodes of the transistor. When the switch is closed, the build-up of the base current to the point of collector current flow and relay energization occurs is determined by the time constant of the RC network. Immediately upon energization of the relay, the relay coil is directly connected to the D.-C. source through the switch, whereby the transistor is inoperative while the relay is energized. Also while the relay is energized, voltage is removed from the RC circuit so that, upon opening the switch connected to de-energize the relay, the delay period can be re-initiated without delay.

Referring to the drawing, single-throw switch 10 has its switch arm 12 connected to the positive terminal of the D.-C. source 14; the other terminal 16 of switch 10 is connected respectively through a resistor 18 and capacitor 20 to the emitter electrode 22 and base electrode 24 of a p-n-p junction transistor 26. A resistor 28 is also connected between the base electrode 26 and a point of reference or ground potential. A relay control coil 30 is connected between the collector electrode 32 and ground.

The relay here shown is provided with an armature 36 which is directly connected through a lead 38 to terminal 16 of switch 10, and an associated pair of contacts 4%, 42, one contact 40 floating and the other contact 42 being connected to the collector electrode 32. Another armature 44 is adapted to be switched between a pair of contacts 46, 48; with armature 44 grounded, output circuit connections through contacts 46, 48 are completed in accordance with the position of armature 44, all in a conventional manner.

Armature 36 in the de-energized condition of the relay coil 30 engages floating contact 40, and upon energization of the coil 30 is placed in engagement with contact 42.

When switch 12 is thrown into contact with terminal 16, the buildup of base current in transistor 26, to the point where collector current flows through coil 30 and actuates the armatures 36, 44, is dependent upon the time constant established by the capacitance of capacitor 29 and the resistance of resistors 18 and 28. When the armatures are actuated, it will be observed that, immediately upon armature 36 being thrown into an engagement with contact 42, coil 30 is directly connected, through contact 40, armature 36, lead 38 and switch 10, to the positive terminal of source 14. Therefore, coil 30 thereafter remains in the energized condition through such direct connection -i.e., transistor 22 is in effect removed from the energizing circuit. When this occurs, differential voltage is removed from the transistor electrodes and from the capacitor 20. That is, the collector and base of transistor 26 are brought to the same full positive voltage as lead 38. Removing such voltage removes the charge on the capacitor 20, because both terminals thereof have full positive voltage applicable thereto so that upon opening switch 10 to de-energize the coil 30, switch 10 can immediately be closed again to initiate the total time delay. Since the transistor is effectively removed from the circuit immediately upon the relay being energized, no power dissipation therefrom occurs While the relay is energized. The following circuit values have been used to achieve a one second delay:

The time delay relay of this invention is less dependent on ambient temperature than the eddy current type. In that type, the large copper plate utilized for eddy current purposes makes the device inherently temperature dependent and prevents efiective compensation. In the circuit of this invention, however, effects of temperature changes on the transistor are readily compensated; for example, a temperature sensitive resistor (not shown) may be placed in series with resistor 18 or resistor 28, or may replace one of such resistors.

With respect to the thermal type of time delay relay, which utilizes a heater element, the time delay is proportional to the square of the source voltage. In the circuit of this invention, however, and as will be apparent from an inspection thereof, the time delay is proportional to the applied voltage. Thus, the time delay relay of this invention is less dependent on voltage than the thermal type. In addition, no heated wires are involved in the circuit of this invention. Additionally, for a given size of time delay relay in accordance aesasae with this invention, adjustment of time delay over a greater range can be made than is possible with prior art time delay relays. Such adjustments obviously may be made by making the capacitor 20, or either of resistors 18, 28, variable.

Although a p-n-p junction transistor has been illustrated and described for use in the circuit of this invention it will be apparent that an n-p-n junction transistor may be employed; in such case, it is necessary only to reverse the voltage, i.e., to connect switch to the negative terminal of source 14.

What is claimed is:

1. In combination, a source of D.-C. voltage, a transistor having emitter, collector and base electrodes, a relay control coil connected between said collector electrode and a point of reference potential, a switch coupled to said emitter electrode, an armature for said coil directly connected to said switch, said source being connected to said switch, means in the emitter-base circuit of said transistor operative upon closing said switch to delay for a predetermined period the establishment or" collector current for energizing said coil, said armature upon energization of the coil moving to a position to establish a direct connection between said collector electrode and said switch, and a return circuit from said transistor base electrode and said relay coil to said source whereby a direct current connection from said source through said coil is established, whereby said switch upon 'being opened to de-energize the coil can immediately be closed to establish the predetermined delay period.

2. A time delay relay comprising a switching device, a relay having an armature directly connected to said switching device, a transistor having its emitter-collector path connected between said switching device and a control coil for said relay, a D.-C. voltage source connected to said switching device, time delay means in the emitterbase circuit of the transistor operative upon closing said switching device to delay current build-up through said transistor and coil for energizing the coil, said armature in the energized condition of the coil providing a direct connection from the coil to said switching device and a return circuit path from the base of said transistor and said coil to said D.-C. voltage source.

3. A time delay relay device comprising a relay having a control coil, a switch, an armature for said relay connected to said switch, a transistor having an emittercollector current path and an emitter-base circuit, said emitter-collector path being connected between said switch and coil, a source of D.-C. voltage connected by one terminal to said switch and by the other to one terminal of said coil, and means in said emitter-base circuit effective upon closing said switch to delay for a predetermined period the establishment of collector current for energizing said coil, and said armature upon energization of said coil being positioned to connect said coil directly to said switch, whereby said coil is kept energized through a direct connection to said source said emitter base circuit including said D.-C. source.

References Cited in the file of this patent UNITED STATES PATENTS Dimond ...Feb. 12, 1952 OTHER REFERENCES 

